A. Field of Invention
This invention pertains to a corrosion prevention system and method of producing the same, and more specifically to a system for protecting a metal substrate from corrosion utilizing a cathodic coating comprising at least one inherently conductive polymer and sacrificial metal particles.
B. Description of the Related Art
One type of coating used to protect metals from corrosion is called a barrier coating. Barrier coatings function to separate the metal from the surrounding environment. Some examples of barrier coatings include paints and nickel and chrome plating. However, as with all barrier coatings, holidays in the barrier coatings leave the metal substrate susceptible to corrosion. Electrochemically active barrier coatings, such as nickel, chrome, and conductive polymer layers, can actually accelerate corrosion of underlying metals at holidays in the coating.
Another type of coating used to protect metal substrates is called sacrificial coatings. The metal substrate is coated with a material that reacts with the environment and is consumed in preference to the substrate it protects. These coatings may be further subdivided into chemically reactive, e.g., chromate coatings, and electrochemically active, or galvanically active, e.g., aluminum, cadmium, magnesium, and zinc. The galvanically active coatings must be conductive and are commonly called cathodic protection.
In the art, a major difficulty has been the creation of a coating that protects like a cathodic system but is applied with the ease of a typical barrier coating system. Furthermore, there are many environmental drawbacks with both traditional barrier and sacrificial methods, from use of high levels of volatile organic compounds to expensive treatment of waste waters produced by plating and subsequent surface preparation for top-coating processes.
The present invention contemplates a new and improved coating system and method of producing the same which overcomes the foregoing difficulties and others while providing better and more advantageous overall results.
In accordance with the present invention, a new and improved cathodic corrosion resistant coating system is provided which may be easily applied in an environmentally friendly, efficient, safe and cost effective way to a metal substrate.
More particularly, the coating system utilizes at least one inherently conductive polymer in combination with galvanically anodic metals dispersed in a resin matrix and applied to a metal substrate to create a cathodic coating which is corrosion resistant.
According to one aspect of the invention, there is provided a method of preparing a coating system adapted for use on an associated metallic substrate, the coating system including a resin binder, an inherently conductive polymer, metallic particles which are anodic to the metallic substrate, and a curing agent. The method includes the steps of mixing the inherently conductive polymer with the metallic particles to form a blend including an inherently conductive polymer/metal particle complex; providing a resin binder selected from the group consisting of water-borne resin systems and solvent-borne resin systems, providing a curing agent; and, mixing the blend, the resin binder, and the curing agent prior to application to the associated metallic substrate.
According to another aspect of the invention, the step of mixing the inherently conductive polymer with the metallic particles includes the steps of mixing the inherently conductive polymer with metallic particles at a process temperature of between 100xc2x0 F. to 220xc2x0 F., inclusive.
According to another aspect of the invention the process temperature is maintained for a sufficient period of time, in order to drive off a predetermined amount of H2-According to another aspect of the invention the step of mixing the blend, the resin binder and the curing agent includes the steps of preparing a Part A resin component by combining the blend with the resin binder; preparing a Part B cure component including the curing agent; and, combining a predetermined amount of the Part A resin component with a predetermined amount of the Part B cure component immediately prior to application to the associated metallic substrate.
According to another aspect of the invention, the step of mixing the blend, the resin binder and the curing agent includes the steps of preparing a Part A resin component including the resin binder; preparing a Part B cure component by combining the blend with the curing agent; and, combining a predetermined amount of the Part A resin component with a predetermined amount of the Part B cure component immediately prior to application to the associated metallic substrate.
According to another aspect of the invention, the method further includes the step of combining a predetermined amount of nano-scale polymerized clay materials with the blend prior to the step of mixing the blend, the resin binder, and the curing agent.
According to another aspect of the invention, the method further includes the step of combining a predetermined amount of nano-scale polymerized clay material into the resin binder prior to the step of mixing the blend, the resin binder, and the curing agent.
According to another aspect of the invention, the step of mixing the inherently conductive polymer with the metallic particles further includes the steps of providing the inherently conductive polymer in an amount from approximately 1% to 35% by volume of the coating system; and, providing the metallic particles in an amount from approximately 5% to 20% by volume of the coating system.
According to another aspect of the invention, there is provided a coating system formed by the method provided above wherein the inherently conductive polymer is at least one member of the group consisting of polyaniline, lignosulfonic acid-doped polyaniline, polypyrrole, polythiopene, polyacetylene, poly (p-phenylene), poly (p-phenylene vinylene), poly (p-phenylene sulfide) and polyaniline substituted with alkyl, aryl, hydroxy, alkoxy, chloro, bromo, or nitro groups; the metal is at least one member of the group consisting of aluminum, cadmium, magnesium, zinc, aluminum alloys, cadmium alloys, magnesium alloys and zinc alloys; the resin binder is at least one member of the group consisting of polyurethanes, epoxies, neutral resins, acidic resins, acrylates, polyesters, and glycidyl acrylates; and, the curing agent is at least one member of the group consisting of sulfonamide, anhydride types, free radical photoinitiators, cationic photoinitiators, and amine types.
According to another aspect of the invention, the at least one inherently conductive polymer comprises between 1% and 35% by volume of the coating system.
According to another aspect of the invention, the metal comprises between 5% and 20% by volume of said coating composition.
According to another aspect of the invention, there is provided a method of protecting a metallic substrate from corrosion including the steps of preparing a coating system comprising a resin binder, an inherently conductive polymer, metallic particles which are anodic to the metallic substrate, and a curing agent wherein the inherently conductive polymer is premixed with the metallic particles at a predetermined process temperature for a predetermined period of time to form a inherently conductive polymer/metal particle complex; preparing a surface of the metallic substrate for adhesion to the coating system; coating the prepared surface with the coating system; and, curing the coating composition to form a corrosion resistant coating on the prepared surface.
According to another aspect of the invention, the coating system is a powder coating system and the step of coating the prepared surface with the coating system includes the step of electrostatically applying the coating system to the associated substrate.
According to another aspect of the invention, there is a coating system formed by the method provided above wherein the inherently conductive polymer is substituted with an electroactive material and may be a member of the group consisting of tannins, o-catechol, p-catechol, 1,4-phenylenediamine, 1,2-phenylenediamine, trimer of aniline (i.e. oxidative polymerization product of 1 mole of 1,4-phenylenediamine and 2 moles of aniline) and several organic dyes.
According to another aspect of the invention, at least one electroactive material comprises between 1% and 35% by volume of the coating system.
One advantage of the present invention is that the claimed process can provide water-borne or solvent-borne coating systems.
Another advantage of the present invention is that the claimed process produces coating systems having improved performance in the areas of corrosion protection, adhesion, hardness, stability, etc. over similar formulations, having the same ratios of the components made in a conventional manner.
Another advantage of the present invention is that a powder coating system utilizing the claimed process may be electrostatically applied.
Another advantage of the present invention is the cost effectiveness of the process. The coating may be produced at a reasonable cost and applied with existing application systems. Use of the inventive coating system will extend service life and reduce the costs associated with corrosion maintenance.
Another advantage of the present invention is that the methods disclosed herein may be used in formulations over a wider pH range than conventional coating systems.
Another advantage of the present invention is the provision of coating compositions utilizing the amine family of hardeners in conjunction with the inherently conductive polymer without de-doping effects.
Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification.